An ultrastructural study designed to elucidate the cellular morphology of the reproductive systems of Schistosoma mansoni, S. haematobium S. japonicum and S. mattheei in unisexual, bisexual and cross infections. Following a study of development of reproductive systems, the fine cellular detail of spermatogenesis, oogenesis, vitellogenesis and egg-shell formation, as well as the cellular architecture of the vitelline gland duct, oviduct, Mehlis' gland, uterus, vas deferens, and seminal vesicle will be determined. Application of the results of this study will provide a means which the effects of chemotherapeutic agents on reproduction and formation of viable eggs can be assessed at a subcellular level.